rsyslog: Send logs to Graylog

Ideally, we would use the log server address provided by DHCP, but for
now, we will just hard-code the destination.

overlay/etc/rsyslog.conf

@@ -1,4 +1,9 @@
 global(workDirectory="/var/lib/rsyslog")
 module(load="imjournal"
        StateFile="imjournal.state")
-*.* @172.30.0.28
+action(
+    type="omfwd"
+    Target="172.30.0.17"
+    Port="514"
+    template="RSYSLOG_SyslogProtocol23Format"
+)